What is the color change observed when acidified potassium dichromate(VI) oxidizes a primary alcohol to an aldehyde?
Answer and explanation
Correct answer: B. From orange to green
- Step 1: The orange dichromate ion (Cr2O7^2-, Cr in +6 oxidation state) acts as a strong oxidizing agent.
- Step 2: Upon reducing the alcohol, it is converted to green chromium(III) ions (Cr^3+), producing a distinct orange-to-green color change.
Answer
From orange to green.
Why not the others: 'From green to purple' is the reverse of a manganate reduction; 'From colorless to deep blue' occurs in starch-iodine tests; 'From yellow to blood red' occurs in thiocyanate iron testing.
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